I just recently upgraded my tank to a 120 gl. I started with base rock and aragonite sand. Nothing live. I choose to start the cycle with shrimp. It has been four weeks and my ammonia has never rose over .50 ppm. It's just staying around there. Also throughout this time I have no nitrites and nitrates. There are a a lot of brown spot showing up on the rock. Does anyone know if I'm doing something wrong? I thought I would get a ammonia spike higher. And it doesn't seem to be dropping or rising. I'm running my light for about 4 hours a day and I also have two mp40s going. Any info would be much appreciated. Thanks, Jason